The present invention relates to a magnetic disk apparatus for recording information, and more particularly, to a servo system of an apparatus using a disk for holding data composed of information magnetized perpendicularly to a film surface.
A magnetic disk apparatus magnetically writes and reads information to and from a rotating disk by moving a head in the radius direction of the disk to accurately position the head over a target data track. The disk has data areas where data is recorded and servo areas where servo patterns used to position the head over a data track are recorded.
FIG. 5 shows an example of servo patterns recorded in a servo area. A reproduction device reproduces servo patterns while traveling from left to right relative to the rotating disk based on FIG. 5. The servo patterns include successive patterns referred to as a synchronize field which is designed to reduce effects of variations in magnetic characteristics of the disk and in the floating height of the head. Also included in the servo patterns are address mark fields each of which is used to detect the time when a track code field begins. The track code field holds track number information which can provide a head position signal to specify a head position out of the entire disk surface. Head positioning information more detailed than a track number is obtained by decoding information recorded in A- to D-burst fields. A- and B-burst fields are shifted in position from C- and D-burst fields by one half the track width. This arrangement is similar to that disclosed in JP-A No. 222468/1983 and is used in many magnetic disk apparatuses.